It turns out that water had worked its way into the battery compartment and corroded the contacts. I lightly sanded them clean, re-assembled and put a thin coat of silicon on the seam. Taylor rules, but that seam should be water proof.
Ironic timing as I was just in a local Leslie's pool supply yesterday and saw that they use a Speedstir for water testing however I noticed that theirs was plugged in on the bottom using a wall wart and ran for longer than the normal amount of time when running from batteries.
Is this a special production item for Leslie's Pool Supply, or is this version also available to the general public as well?
SpeedStir is a must and I started using a Sample Sizer which made testing even easier. You need the Taylor Calibrated Cylinder too. I bought several cylinders with one cylinder dedicated for FC testing.